Admissibility of Evidence in Criminal Proceedings: Lessons (and Problems) from the ‘Data Retention Saga’

Admissibility rules lie at the crossroads of a number of essential questions that haunt whoever approaches the matter of evidentiary law, or, more broadly, inquires about the meaning of ‘effective protection’ of fundamental rights in all proceedings that see public authorities pitted against private individuals. In a context where investigations are increasingly data-driven, and in which neither standards for the collection of digital evidence, nor investigative techniques that use digitalization and automation are clearly framed in legal systems, the protection of fundamental rights is more and more depending on the keeping of the rules of admissibility. This chapter will principally examine the rules draft ed by the European courts, and in particular by the Court of Justice of the European Union (CJEU). As the CJEU has mostly tackled the issue of admissibility within a series of decisions – it might be called a ‘saga’ – concerning data retention and privacy rights (see section 2), this further limits the scope of the analysis. On the one hand, this chapter will pay specific attention to admissibility rules drafted for a particular form of data, that is metadata of communications (traffic data, IP addresses and subscriber information). Thanks to the chosen viewpoint, the discussion will highlight an aspect that is often not fully considered when looking at admissibility from a purely criminal law perspective, that is the (unclear) relationship between privacy and fair-trial violations, and the extent to which these aspects could, or should, overlap (section 3). At the same time, the European case law on admissibility exacerbates a classic theme, that is the difficulty, perhaps the impossibility, of drawing a clear line between preventive and post-factum investigations. The complexity of the problem will be exemplified in this chapter by looking at the field of financial supervision, a matter where, as it will be argued, the approach of the CJEU shows all its limitations (section 4) . Finally, some conclusive considerations will contextualise the lacunas of the applicable case law against a recent proposal for a Directive on admissibility of evidence, trying to delineate a possible way forward in a jungle of decisions and enforcement systems that make admissibility rules as essential as they are difficult to define (section 5).